Orientation dependence of gas sensing properties of TiO sub(2) films

Highly oriented polycrystalline TiO sub(2) films were grown on sapphire substrates with various orientations using rf magnetron sputtering, and the effects of the crystallographic orientation on the H sub(2) and CO gas sensing performance were investigated. The orientation of the TiO sub(2) films was strongly dependent on the substrate orientation such that (1 0 1)/(1 0 0), (1 0 1), (0 0 1), and (1 0 0) oriented TiO sub(2) films were formed on [image] (a-cut), [image] (r-cut), [image] (m-cut), and (0 0 0 1) (c-cut) Al sub(2)O sub(3), respectively. A fine surface feature developed in the films grown on [image] and [image] Al sub(2)O sub(3) and a rather rough surface was obtained in case of the [image] Al sub(2)O sub(3) substrate. The deposited TiO sub(2) films showed a short response time and high gas response toward H sub(2) and CO balanced with N sub(2). The TiO sub(2) film grown on [image] Al sub(2)O sub(3) exhibited the highest H sub(2) gas response possibly due to the (1 0 0) orientation and high surface area. The (0 0 1) orientation of TiO sub(2) showed the highest selectivity toward H sub(2) against CO.